Abstract: Is it possible to prove that two DNA-fingerprints match, or that they do not match, without revealing any further information about the fingerprints? Is it possible to prove that two objects have the same design without revealing the design itself? In the first part of this talk, I will illustrate examples of "zero knowledge" proofs of physical properties, and discuss an approach to formally modeling and proving security of interactive computations involving physical inputs and/or behavior. In the second part, I will present a general technique for computing any multi-party functionality over physical inputs. The technique relies on tamper-proof hardware and achieves security with input-dependent abort (i.e. an adversary learns at most 1 additional bit about the inputs).